In order to improve the conversion efficiency of amorphous silicon solar cells, the properties of transparent conductive oxide (TCO) films were optimized. Highly textured TCO films of tin oxide doped by fluorine, which have high optical confinement effect, were prepared by an atmospheric pressure CVD (chemical vapor deposition) method, and were designated as Type-U. The surface morphology of Type-U TCO was controlled to prevent a drop in open circuit voltage, which was highly textured TCO. The texture shape of the obtained Type-U TCO was characterized by uniform pyramidal facets without too steepened structure. As a consequence of evaluation as solar cells, it was shown that the Type-U TCO is effective for improving the conversion efficiency by fulfilling the high open circuit voltage as well as the high short circuit current. It was also suggested that the uniform surface structure of Type-U TCO contributes to lower defect formation in the amorphous silicon layer, which is a main cause of the open circuit voltage. 17 refs., 8 figs., 2 tabs.